Color of meat
1.Meat is one of the most important factors affecting the consumer`s decision to purchase fresh and
processed meat products.
2.Myoglobin is the predominant meat pigment and accounts for 80% of the meat pigment.

• Myoglobin consists of a protein called a globin and the non protein portion as heme ring.
• The heme portion is important as color of meat predominantly depends
  on the chemical state of the iron present in the heme ring.
• The heme group of myoglobin is planar structure with iron atom centrally located.
• Iron atom is a transition metal capable of existing as ferric( oxidized) and ferrous ( reduced) forms. It has
  6 coordination sites.
• These sites are available for chemical bonds.
• Out of 6 the 4 of these have iron atom attached with heme, the fifth connects iron atom to amino acid
  chain of globin protein and sixth to coordination site.
• The coordination site is available for binding of a variety of chemical groups.
• The chemical group bound to sixth site ( i.e. known as ligand )the oxidation state of heme iron determines
  the color of meat.
• The oxidation state of heme iron affects the color of meat.
• The oxidation state determines which molecule will bind at sixth site of heme iron.
• The ferrous myoglobin or deoxymyoglobin 9 purplish red 0 bind O2 at the sixth site and form oxymyoglobin
  (cherry red ). This is oxygenation and not oxidation ( loss of electrons).
• The oxidation occurs in myoglobin when ferrous form is converted to ferric form and leads to formation of
  metmyoglobin ( brownish red 0 in fresh meat. But the ligand in this case is water molecule.

Therefore there could be variable colors depending upon the oxidation state of central; iron atom and some of
the probable ones could be(click). When meat is subjected to curing treatments the color reactions could
be like these.

3. The myoglobin content varies with species, age, sex muscle and physical activity.

• Beef – bright , cherry red
• Fish – gray- white to dark red
• Horse – dark red
• Lamb and mutton – light red to brick red
• Pork – grayish pink
• Poultry – gray – white to dull red
• Veal– brownish pink

4. Approximately 20 % of the pigment in meat is hemoglobin . However, the bulk of hemoglobin is found in the
arteries,veins and capillaries.
5. The normal color of the surface of fresh meats in an oxygen environment is bright red/pink due to oxymyoglobin.
As oxygen penetrates into muscle, it is utilized to oxidize reduced compounds ( co-enzymes). This results in an
oxygen gradient ranging from saturation on the surface to zero a few centimeters in the muscle. At low partial
pressures of oxygen metmyoglobin is formed. The effect of oxygen is shown in the figure below —
6. The chemical state of myoglobin affects the color– Oxidized myoglobin Reduced myoglobin Heme
Enzyme activity.
7. There are certain factors that affect the color of pigments

• oxidation state of Iron - depending upon if
  ferrous Fe++ (red or purple)
  ferric Fe+++ (red or brown)
• Ligand - depending upon if
  none Fe++ (purple)
  strong ( covalent ) shall be red
  weak ( ionic ) shall be red - brown
• Physical state of protein - depending upon if
  native will be red purple or brown
  denatured will be pink or brown
• Porphyrin integrity - depending upon if
  intact color will be red purple or brown
  substituted color will be green
  cleaved color will be green brown or yellow

Color changes can occur when conditions are created favoring that reaction or when chemicals are
available to bind with myoglobin.

• Discoloration of meat–
  Apart from the reasons discussed above there could be certain other reasons which could lead to
  discoloration of meat.
• PSE meat has a pale color due to presence of more water in the on the surface of the meat and the
  low pH causes denaturation of proteins.
• The DFD meat appears to be more darker . This is due to increased bound water in meat which minimizes
  the white light reflection and color absorption is enhanced. The dark cutting meat also has a high rate of
  oxygen using enzyme activity.
  due to high pH this in turn reduces the proportion of the pigment in the oxymyoglobin.
• The color of the meat also serves as an indicator of the quality of the meat. The color is to an extent
  indicator of physical, chemical and bacterial contamination.
• The microbes change the physiological environment by changing the pH and by producing amino acids and
  amines. They may also produce compounds which may react with the heme pigments to produce other
  colors. Catalase negative bacteria produce hydrogen peroxide that results in a green color.
• Microorganisms change the color also by producing pigments themselves.
• Salt works as a prooxidant for heme pigment oxidation and thereby also influences the color.
• Light can cause the dissociation of oxygen from the heme which may result in the fading of fresh meat color.
• Cooking causes protein denaturation and the browning reactions. During cooking the heme pigment protein
  denatures and the iron undergoes oxidation to the ferric state and ability of the pigment to complex
  oxygen is lost.

Color shelf life extenders–
1.Application of antioxidants like ascorbic acid, citric acid, alpha tocopherol etc. may extend the color shelf life.
2. Application of nitrites and nitrates .

The table as seen above gives by and large a complete picture of composition of meat. The meat serves
as a source of proteins, fats, carbohydrates, minerals and vitamins. A lean meat cut has a composition
as given below—

protein — 20% fat — 3% moisture — 75% ash — 1%

Percent of RDA ( recommended daily allowance ) by a 3 ½ oz serving of cooked meat shall provide
following nutrients

• protein - 60
• calories - 15
• calcium - 1
• iron - 20
• phosphorus - 25
• magnesium - 8
• thiamin - 42
• riboflavin - 30
• niacin - 35
• vitamin B6 - 20
• vitamin B12 - 60